Did you read anything about kuru beforehand? It’s contracted by ritual eating in general rites. They also have no means of diagnosing prion infection in a corpse, which is why people would eat brain tissue with prions. It didn’t spontaneously form in those victims, it was in the corpse. Overall, it could be avoided by just not eating infected meat, hence why Papua New Guinea did not collapse from kuru - it was rare to get it, and once the mode of transmission was known, it was much easier to avoid.

Chronic wasting disease was first observed in deer in the 1960s, and there is nothing actually confirming it’s exact origin. it was first noted in deer herds being researched in Colorado, and as far as I am reading, it did not jump from sheep to deer.

We do actually regulate mad cow disease, going as far as culling entire herds of livestock and disposing of the meat. Outbreaks happen, yes, but we are keeping that spread down. This is also in meat that we sell at an insane scale, one which would not be replicatable with human meat without slavery.

With human donated meat, it’s very unlikely you would get prions. Again, you are way more likely to get it from cow meat and deer meat.